1. Field of the Invention
This invention relates to a zoom lens and an electronic imaging apparatus using the zoom lens, and in particular, to an electronic imaging apparatus, including a video camera or a digital camera, in which a compact design and a slim design regarding a depth direction of a zoom optical system are attained.
2. Description of Related Art
Recently, special attention has been devoted to digital cameras (electronic cameras) as the next generation cameras that are an alternative to cameras for silver halide 35 mm films (135 formats). The digital cameras have come to have many categories in a wide range from a high-function type for business use to a popular portable type.
The greatest obstacle to a reduction in depth of a camera is the thickness of an optical system, notably extending from the most object-side surface of a zoom lens system to an imaging surface. The main current of a slim design technique for a camera body in recent years is to adopt a so-called collapsible lens barrel in which the optical system protrudes from the camera body in photography, but when the camera is carried, the optical system enters the camera body. To construct a zoom optical system of a high variable magnification ratio, it is known that an arrangement made to include, in order from the object side, a first lens unit with positive power, a second lens unit with negative power, and an aperture stop is effective. Such arrangements are disclosed, for example, in References 1-5 described below.                Reference 1: Japanese Patent Kokai No. Hei 1-201614        Reference 2: Japanese Patent Kokai No. Hei 5-27167        Reference 3: Japanese Patent Kokai No. 2002-62478        Reference 4: Japanese Patent Kokai No. 2003-255228        Reference 5: Japanese Patent Kokai No. 2003-295059        
However, there are particular demands that a zoom ratio of at least 5 is required, a thickness corresponding to a depth is made smaller, the total length of the optical system and housing size are reduced, and in a collapsible type, compactness of the entire body should be attained by reducing the diameter of a front lens to make the lens barrel compact.
Generally, as an angle of view at a wide-angle position or the zoom ratio is increased, the diameter of the front lens relative to an image height becomes large and the total length of the zoom optical system in photography increases. In particular, when the angle of view at the wide-angle position is widened or the total length of the zoom optical system in photography at the wide-angle position is increased, the light-emitting position of a stroboscopic lamp must be separated from the optical axis of a photographic lens. This leads to oversizing of the body and the complication of the structure.
Recently, digital cameras in which an image of an object is photographed through a solid-state image sensor, such as a CCD (charge couples device) image sensor, to digitally process and record image data on a still image or movie image of the object have already been popularized.
Techniques relating to optical systems in which the collapsible lens barrel is adopted are proposed, for example, by References 6-8 listed below.                Reference 6: Japanese Patent Kokai No. Hei 11-194274        Reference 7: Japanese Patent Kokai No. Hei 11-287953        Reference 8: Japanese Patent Kokai No. 2000-9997        
The optical system stated in each of References 6-8 includes, in order from the object side, a first lens unit with negative refracting power and a second lens unit with positive refracting power so that, upon zooming from the wide-angle position to the telephoto position, they are moved together.
In each optical system of References 6-8, however, the optical system of a zoom lens is linear and thus the shifting portion of the optical system is bulky. This causes the problem that when the collapsible lens barrel is adopted, time for rising into a state of use from a state where lenses are incorporated (that is, a shifting time of the optical system) is taken, which is unfavorable for practical use. Moreover, there is another problem that the movement of the most object-side lens unit in zooming is unfavorable for water- and dust-proof design.
To obtain a camera which has no time for rising into a state of use of the camera (the shifting time of the lenses), is favorable for water- and dust-proof design, and is very small in thickness in a depth direction, techniques relating to zoom optical systems in which the optical path (the optical axis) of the optical system can easily be bent by a reflecting optical element, such as a mirror, are proposed, for example, by References 9-12 described below.                Reference 9: Japanese Patent Kokai No. 2004-4533        Reference 10: Japanese Patent Kokai No. 2004-564343        Reference 11: Japanese Patent Kokai No. 2003-202500        Reference 12: Japanese Patent Kokai No. 2004-37967        
The optical system set forth in each of References 9-12 adopts the structure that the optical path (the optical axis) of the optical system is bent by the reflecting optical element such as the mirror, thereby reducing a length in the direction of the incident optical axis of the zoom lens. Specifically, the optical path provided behind the reflecting optical element is bent in a longitudinal or lateral direction of the camera body, and thereby the dimension in the depth direction is decreased as far as possible.
However, in order to attain the compact design of the digital camera, a smaller-sized and higher-performance zoom lens is required.